Most of that is due to same old/same old.

And technically there's FOUR! GaoGorilla, GaoKong (Hey Den-O, when I get to doing the Wild Force/Transformers story, should I do that as a powered up Gorilla or a totally new Wildzord?), GaoApe, and GaoUtan.

Yeah, pretty BS. Doesn't bug me as much as the Panda. Pandas don't look like that!

Well in a rare transitional period, Gaoranger got the obligatory black repaint PLUS a movie repaint/remold. GaoKong has a different face from GaoGorilla, as well as its own combo with GaoKnight.
GaoApe is.. um.. black. To go with the Black GaoKing. Later accompanied by a Black GaoElephant. I dunno what order they came in, but I'd think Black GaoElephant was released to add value to the TRU-exclusive GaoKnight set, and then someone realized they were one Power Animal away from a fully black GaoKnight and then they made GaoApe.

Actually there are 4 repaints even! There's also a silver chrome promo/Lucky draw Gao Gorilla!
Gaoutan unfortunately has no figure, but we can surmise that a reddish brown Gao Gorilla would have been the route to go. The art book at least mentions that much.

True. It's a rare honor for this show. Gao Kong does feature the new Gao Knight headsculpt. And Gao Ape is actually a repaint of Kong, not Gorilla, my mistake. Because it also features the Knight headsculpt. It was released as an exclusive mail in type release along side the sentai mecha 75-01 collection art book. I know it came out after Black Gao King but I don't know the specific release order of the others.

It's specifically stated to be orange. Which makes sense; unlike some of the colored animals, Orangutans DO have subspecies that are orange.

Just because I'm curious, was the Isis Megazord ever released Stateside?